The aim of this study is to measure the turnover of two formulations of cyclosporin: Cyclosporine (Sandimmune-SM, the old formulation) and Neoral (NL-the new formulation). The patients who will receive NL are those for whom the decision to switch to the new formulation has already been made on clinical grounds. The information obtained from this study will benefit in the design of dosing regimens for patients in general who are candidates for conversion from SM to NL.